In order to obtain a streak-free fabric, these thread guidance channels formed from plates must pass in and out of the shed at an adequate distance from the last fastened weft thread. However, in known looms this distance leads to large sley strokes, and therefore considerable shed heights. This in turn leads to limits being placed on performance, due to high inertia forces with wear, noise and high energy requirements.
Attempts have thereforebeen made to provide looms which, despite a limited sley travel, permit an adequate spacing of the weft thread guide channel plates during insertion.
Known devices of this type according to W. German published applications Nos. 2,631,593 and 2,454,878 attempt to solve this problem by a separate movement of the onepiece thread guide channel and the sley. The separate movement of the complete channel involves large strokes, so that new disadvantages occur.
Other known devices according to W. German published applications Nos. 1,932,836, 2,160,998, 2,056,992, 2,806,301, Swiss Pat. No. 586,298 or Swiss Pat. No. 438,167, operate with a movement of parts of the thread guide channel superimposed on the sley movement but do not have the features permitting a reduction of the sley travel. Their function is exclusively the opening and closing of the thread guide channel.
Another known device according to W. German published applications No. 2,420,368, with a movement of the entire thread guide channel superimposed on the sley movement, also had disadvantages from the performance and fabric quality standpoints. The thread guide channel used is dependent on the reed density and therefore on the fabric quality to be produced. As a result, in the case of changes, it is necessary to change the reed with the appropriate thread guide channel, which is extremely uneconomic. In addition, the thread guide plates for the weft threads to be moved through the shed leads to a restricted opening with increased thread friction, leading to additional material stressing and weft thread breaks with weaving errors.